The present invention relates to a fluid dynamic bearing apparatus which relatively rotatably supports a shaft member by a lubricating film of a fluid produced in a bearing gap.
Fluid dynamic bearing apparatuses are recently used as bearings for motors mounted on information appliances and various other electrical machinery and apparatuses because of their excellent rotational accuracies, high-speed rotation properties, quietness and other properties. More specifically, fluid dynamic bearing apparatuses are used as bearing apparatuses for spindle motors mounted on information appliances such as for HDD and like magnetic disk apparatuses, CD-ROM, CD-R/RW, DVD-ROM/RAM and like optical disk apparatuses, and MD, MO and like magneto-optic disk apparatuses, and as bearing apparatuses for polygon scanner motors for laser beam printers (LBP), collar wheel motors of projectors, and motors such as fan motors and the like.
Fluid dynamic bearings of this type are roughly classified into: hydrodynamic bearings comprising a hydrodynamic pressure producing part for producing hydrodynamic pressure action in a lubricating fluid in a bearing gap; and so-called cylindrical bearings (bearings having a bearing cross section in a perfect circle shape) comprising no hydrodynamic pressure producing part.
For example, in a fluid dynamic bearing apparatus integrated into a spindle motor of HDD and like disk drive units, a radial bearing portion which supports a shaft member in the radial direction and a thrust bearing portion which supports the shaft member in the thrust direction are both constituted of hydrodynamic bearings in some cases. FIG. 8 shows an example of such a constitution, wherein a radial bearing portion R which supports a shaft member 20 in the radial direction in a non-contact manner, and a thrust bearing portion T which supports the shaft member in the thrust direction in a non-contact manner are provided. As a bearing of this radial bearing portion R, hydrodynamic bearings in which grooves (hydrodynamic grooves) for producing hydrodynamic pressure are provided on the inner circumferential surface of a cylindrical sleeve member 80 are known. Known examples of the thrust bearing portion T include hydrodynamic bearings in which hydrodynamic grooves are provided on both end faces of a flange portion 20b of the shaft member 20, or on the faces opposing these (an end face 81 of the sleeve member 80, an end face 71a of a thrust member 71 fixed on a housing 70, etc.) (for example, refer to Japanese Unexamined Patent Publications No. 2003-239951, No. 2003-336636, and No. 2003-65324).
As is often the case with the hydrodynamic bearing apparatuses of this type, the sleeve member 80 is usually fixed in a predetermined position of the inner periphery of the housing 70, and a sealing portion 100 is installed in an opening portion of the housing 70 to prevent leakage of a lubricating oil poured into the inner space of the housing 70 to the outside. The inner circumferential surface of the sealing portion 100 forms a sealing space S between itself and the outer circumferential surface of the shaft member 20, and the capacity of this sealing space S is set to be greater than the amount of a change of the capacity of the lubricating oil filling the inner space of the housing 70 caused by thermal expansion and contraction within the operating temperature range. Therefore, even when there is a change in the capacity of the lubricating oil due to a change in temperature, the oil level of the lubricating oil is always maintained within the sealing space (refer to Japanese Unexamined Patent Publication No. 2003-65324).